Wireless systems employing multiple antennas at the transmitter and at the receiver (MIMO) increase the capacity of the wireless channel. One major concern in the implementation of these systems is the high cost owing to the price of the RF chains (low noise amplifiers, analog-to-digital converters, etc.) attached to each antenna. On the other hand, the additional antenna elements are usually inexpensive, and the additional digital signal processing becomes ever cheaper. A low cost, low complexity solution to this problem is to choose a subset of antennas M out of N antenna signals (either at one or both link ends), down-converted, and processed. This reduces the number of required RF chains from N to M, and, thus, leads to significant savings. The savings come at the price of a (usually small) performance loss compared to the full-complexity system.
Receiver antenna selection and combining has been well studied in literature on RAKE receivers. On the other hand, transmitter antenna selection is particular interest to down link transmission where the access point (AP) usually have larger space and can install large number of antennas. Transmitter antenna selection over flat fading channel has been suggested in conventional systems. For example, D. A. Gore, R. W. Heath and A. J. Paulraj, “Transmit selection in spatial multiplexing systems”, IEEE Comm. Letters, Vol. 6, No. 11, November 2002, pp. 491-493, provide two selection algorithms based on the statistical information of the channel correlation. The first algorithm maximizes the average throughput, and the second one maximizes average error probability. Both algorithms provide the same selection results.
Further, R. W. Heath, S. Sandhu and A. Paulraj, “Antenna selection for spatial multiplexing systems with linear receivers,” IEEE Comm. Letters, Vol. 5, No. 4, April 2001, pp. 142-144, analyze antenna selection performance for spatial multiplexing systems with linear receivers using the instantaneous channel knowledge. Three selection criteria, namely maximization of post-processing SNR, maximization of minimum singular value and maximization of capacity are compared.
In addition, R. S. Blum and J. H. Winters, “On optimum MIMO with antenna selection,” IEEE Comm. Letters, Vol. 6, No. 8, August 2002, analyze the optimality of MIMO with antenna selection. However, all of the above approaches are focused on the flat fading channels.